A.mongotop

B.mongostat

C.constats

D.dbstats

A.individual language drivers

B.mongo shell

C.mongos

D.mongod

A.Clients read from the nearest member of a replica ser by default

B.Operations on the primary are recorded in a capped collection called the oplog

C.Members of a replica set may replicate data from any other data-bearing member of the set by default

A.db. posts.createIndex({^comments.author" :1});

B.db.posts.createIndex({^commerits.author";-!});

C.db.posts.createIndex({^comments.$.author":-l});

A.A

B.A, B

C.B, C

D.A, B, C